Solar thermal collectors are devices for converting sunlight into heat. They fall into one or more categories including tracking (wherein the collector physically moves in order to follow the path of the sun thereby to increase efficiency), non-tracking, and concentrating (wherein optics are used to concentrate the rays of the sun to increase performance). One other characteristic of solar thermal collectors is their use of heat retention strategies to reduce heat loss to the environment to increase efficiency.
Hybrid solar thermal collectors incorporate a photovoltaic element in the form of a solar cell to allow for the simultaneous production of heat and electricity.
US Patent Application No. 20110120452 describes a solar thermal collector with an approach to heat retention that relies on the properties of the heat transfer fluid (HTF). In that design sunlight passes through the heat transfer fluid, which is transparent to visible radiation, and is incident on a porous light absorbing plate which is heated as a result. The heat is transferred from the HTF to the plate as it passes through the plate. Additional heat, which would normally be lost via thermal radiation from the plate, is absorbed by the HTF because the HTF is opaque to infrared radiation. This formerly lost heat is therefore retained by the collector and efficiency is improved.